The subject of conditioning air for increasing the comfort of human beings has been the subject of intense study for many years from which it has been learned that for optimal results attention must be paid to a number of factors other than merely heating or cooling the air.
For example, in The Handbook of Engineering Fundamentals, John Wiley & Sons, Third Edition 1975, air conditioning is defined broadly as the simultaneous control of temperature, humidity, motion, and purity of air to meet the requirements of human comfort. Some of the principal factors affecting human comfort and welfare as influenced by air environment are the (1) air dry-bulb temperature, (2) humidity, (3) motion, (4) distribution, (5) dust control, (6) bacteria content, and (7) odors. Other factors which may influence comfort, but the effects of which are not so well established at the present time, are (8) light, (9) ozone content, (10) ionic content, and (11) pressure. Human occupancy of a confined space produces a number of important alterations in the properties of the air: (1) oxygen content is decreased slightly; (2) carbon dioxide content is increased slightly; (3) products of decomposition, usually accompanied by odors, are given off; (4) air temperature is raised; (5) humidity is increased by evaporation of moisture from the skin and the lungs; and (6) the number of positive and negative ions in a unit volume of the air is decreased. Also, it has been found that in an occupied space, at least 10 cubic feet of fresh air per minute per person should be provided to adequately remove body heat, body odors, and products of respiration.
Still further, the American Society of Heating and Ventilation Engineers provides that the relative humidity shall not be less than 30 percent, nor more than 60 percent, and that the effective temperature shall range between 64.degree. and 69.degree. Fahrenheit when cooling or dehumidification is required.